1. Field of the Invention
This invention relates generally to methods and apparatus for actuating a tool in a borehole. More particularly, the invention relates to orienting or positioning a tool in a borehole and, once properly oriented, setting the tool in a fixed position. Still more particularly, the invention relates to an actuation apparatus that uses a pressure differential in a conduit carrying a fluid flow to actuate a downhole hydraulic tool.
2. Background of the Related Art
Hydraulically-actuated tools such as packers and anchor assemblies have long been used in the drilling industry. A tool often used in conjunction with anchors or packers is a whipstock. A whipstock includes an inclined face and is typically used to direct a drill bit or cutter in a direction that deviates from the existing borehole. The combination whipstock and anchor (or packer) is frequently termed a sidetrack system. Sidetrack systems have traditionally been used to mill a window in the well casing, and thereafter to drill through the casing window and form the lateral borehole.
Originally, such a sidetrack operation required two trips of the drill string. The first trip was used to run and set the anchor or packing device at the appropriate elevation in the borehole. With the anchor or packer in place, the drill string was then removed from the well and a survey was made to determine the orientation of a key on the upper end of the anchor-packer. With that orientation known, the whipstock was then configured on the surface so that when the whipstock engaged the anchor-packer in the borehole, it would be properly oriented. So configured, the whipstock, along with an attached cutter, was then lowered in the borehole on the drill string and secured to the anchor-packer. Once connected to and supported by the packer, the whipstock directed the cutter so that a window would be milled in the casing of the borehole at the desired elevation and in the preselected orientation. This two-trip operation for setting the anchor-packer and then lowering the whipstock and cutter is time-consuming and expensive, particularly in very deep wells.
To eliminate the expense associated with two trips of the drill string, an improved sidetrack system was developed which required only a single trip. Such a system includes a whipstock having an anchor-packer connected at its lower end, and a cutter assembly at its upper end connected by a shearable connection. Using such a system, the whipstock is oriented by first lowering the apparatus into the cased borehole on a drill string. A wireline survey instrument is then run through the drill string to check for the proper orientation of the suspended whipstock. After the whipstock is properly oriented in the borehole, and the anchor-packer set, the drill string is then lowered causing the cutter assembly to become disconnected from the whipstock. As the cutter is lowered further, the inclined surface of the whipstock cams the rotating cutter against the well casing, causing the cutter to mill a window in the casing at the predetermined orientation and elevation.
To be contrasted with wireline devices, there exist today a variety of systems that are capable of collecting and transmitting data from a position near the drill bit while drilling is in progress. Such measuring-while-drilling (xe2x80x9cMWDxe2x80x9d) systems are typically housed in a drill collar at the lower end of the drill string. In addition to being used to detect formation data, such as resistivity, porosity, and gamma radiation, all of which are useful to the driller in determining the type of formation that surrounds the borehole, MWD tools are also useful in surveying applications, such as, for example, in determining the direction and inclination of the drill bit. Present MWD systems typically employ sensors or transducers which, while drilling is in progress, continuously or intermittently gather the desired drilling parameters and formation data and transmit the information to surface detectors by some form of telemetry, most typically a mud pulse system. The mud pulse system creates acoustic signals in the drilling mud that is circulated through the drill string during drilling operations. The information acquired by the MWD sensors is transmitted by suitably timing the formation of pressure pulses in the mud stream. The pressure pulses are received at the surface by pressure transducers which convert the acoustic signals to electrical pulses which are then decoded by a computer.
MWD tools presently exist that can detect the orientation of the drill string without the difficulties and drawbacks described above that are inherent with the use of wireline sensors. However, known MWD tools typically require drilling fluid flow rates of approximately 250 gallons per minute to start the tool, and 350 to 400 gallons per minute to gather the necessary data and transmit it to the surface via the mud pulse telemetry system. The conventional bypass valves used in present-day sidetrack systems for circulating drilling fluid and transporting a wireline sensor to the whipstock tend to close, and thereby actuate the anchor-packer, at flow rates of approximately 100 gallons per minute, or even less. Thus, while it might be desirable to combine MWD sensors in a sidetrack system, if drilling mud was circulated through the drill string at the rate necessary for the MWD tool to detect and communicate to the driller the orientation of the whipstock, the bypass valve would close and the anchor-packer would be set prematurely, before the whipstock was properly oriented.
An improved apparatus for setting a hydraulically actuatable downhole tool in a borehole is disclosed in U.S. Pat. No. 5,443,129, assigned on its face to Smith International, Inc. and that patent is incorporated herein by reference in its entirety. The ""129 apparatus utilizes a bypass valve located in the run-in string below the MWD device and above the cutter. The valve is in an open position while the MWD device is operating thereby diverting fluid flow and pressure from the tubular to the annulus without creating a pressure sufficient to actuate a downhole tool. Upon completion of operation of the MWD device, the bypass valve is remotely closed. Thereafter, selectively operable ports in the cutter are opened and the tubular therebelow is pressurized to a point necessary to actuate the tool. While the apparatus of the ""129 patent allows operation of a MWD device without the inadvertent actuation of a downhole tool, the bypass valve is complex requiring many moving parts and prevents the continuous flow of fluid through the cutter. Additionally, fluid borne sediment tends to settle and collect in the cutter.
There is a need therefore, for a single trip sidetrack apparatus permitting a continuous flow of well fluid therethrough while allowing the actuation of a hydraulically actuated tool at a predetermined position in the borehole. There is a further need therefore, for a single trip sidetrack apparatus that includes a MWD device that can be continuously operated. There is a further need for a single trip sidetrack apparatus that does not depend on a value to prevent inadvertent actuation of a downhole tool. There is yet a further need for an actuation apparatus that allows fluid to flow therethrough before and during actuation of a downhole tool.
The invention provides an apparatus for actuating a downhole tool by utilizing a pressure differential created by fluid flowing through a conduit. The conduit is in communication with a pressure sensing line that is selectively exposable to areas of the conduit having different pressures. By exposing the pressure sensing line to a portion of the conduit having a predetermined pressure therein, the pressure sensing line causes actuation of a hydraulic tool therebelow.
In one aspect of the invention, fluid flowing through the conduit is utilized to operate a MWD. Thereafter, the pressure line is exposed to a predetermined pressure and the hydraulic tool is actuated. In another aspect of the invention, the pressure in a given area of the conduit is increased due to a restriction therein. At a predetermined time, the pressure line is exposed to the given area and pressure therein actuates the hydraulic tool. The invention includes a running assembly on a drill string, the assembly including an MWD, a pressure changing and sensing mechanism and a cutter.